Update existing tests and test actual pruning

test/retention/docker-compose.yml

@@ -0,0 +1,22 @@
+services:
+  backup:
+    image: offen/docker-volume-backup:${TEST_VERSION:-canary}
+    restart: always
+    environment:
+      BACKUP_CRON_EXPRESSION: 0 0 5 31 2 ?
+      BACKUP_RETENTION_PERIOD: 15s
+      BACKUP_PRUNING_LEEWAY: 1s
+    volumes:
+      - app_data:/backup/app_data:ro
+      - /var/run/docker.sock:/var/run/docker.sock
+      - ${LOCAL_DIR:-./local}:/archive
+
+  offen:
+    image: offen/offen:latest
+    labels:
+      - docker-volume-backup.stop-during-backup=true
+    volumes:
+      - app_data:/var/opt/offen
+
+volumes:
+  app_data:

test/retention/run.sh

@@ -0,0 +1,28 @@
+#!/bin/sh
+
+set -e
+
+cd "$(dirname "$0")"
+. ../util.sh
+current_test=$(basename $(pwd))
+
+export LOCAL_DIR=$(mktemp -d)
+
+docker compose up -d --quiet-pull
+sleep 5
+
+docker compose exec backup backup
+
+sleep 20
+
+if [ $(ls -1 $LOCAL_DIR | wc -l) != "1" ]; then
+  fail "Unexpected number of backups after initial run"
+fi
+pass "Found 1 backup files."
+
+docker compose exec backup backup
+
+if [ $(ls -1 $LOCAL_DIR | wc -l) != "1" ]; then
+  fail "Unexpected number of backups after initial run"
+fi
+pass "Found 1 backup files."